Solid state lithium electrochemical cells are known in the art. The cells typically consist of a lithium, or a lithium-based metal anode, a lithium ion-conducting solid electrolyte and a cathode containing a lithium ion insertion electrode material.
An insertion electrode material is capable of acting as a cathode by virtue of its ability to reversibly accommodate lithium ions physically inserted into its structure during the discharge of the cell and subsequently removed therefrom during charging of the cell. Such insertion, or intercalation, electrode materials as V.sub.2 O.sub.5, TiS.sub.2, V.sub.6 O.sub.13, LiCoO.sub.2 have satisfactory specific energy densities of about 300-900 Wh/kg and mid-discharge voltages of about 2-3 volts.
Among the transition metal compounds, several transition metal oxides have been very well studied as electrode materials, including V.sub.2 O.sub.5. However, V.sub.2 O.sub.5 possesses several drawbacks. The amount of lithium and its ease of insertion in the cathode material depends on the crystallographic lattice structure of the material, and the number and nature of its lattice defects, as well as on the composition of the material. Therefore, materials of the same empirical formula, VO.sub.y, will differ remarkably in their properties as cathode material. Solid lithium electrochemical cells using V.sub.6 O.sub.13 as the active cathode material are also well studied. K. West et al., J. Power Sources, 14:235-246 (1985), studied V.sub.6 O.sub.13 as a cathode material for lithium cells using polymeric electrolytes. They found that the lithium insertion reaction was reversible in the composition interval Li.sub.x V.sub.6 O.sub.13, where 0.ltoreq.x.ltoreq.8. The high stoichiometric energy density for the ultimate composition Li.sub.8 V.sub.6 O.sub.13, 890 Wh/kg, is very favorable for battery applications.
P. A. Christian et al., U.S. Pat. No. 4,228,226 suggest that lithiated vanadium oxides of the empirical formula Li.sub.x VO.sub.2+y where 0&lt;y.ltoreq.0.4, may be prepared chemically by treatment of VO.sub.2+y with n-butyllithium in hexane. The use of Li.sub.x VO.sub.2+y, chemically manufactured as aforesaid, as the positive electrode material, permits the manufacture of cells in the discharged state.
A number of methods of preparation of vanadium oxides of various stoichiometry have been reported, including the production of V.sub.6 O.sub.13 by the thermal decomposition of ammonium vanadate (NH.sub.4 VO.sub.3) at a controlled rate in an inert atmosphere, such as argon or nitrogen at a temperature of approximately 450.degree. C.; and the production of V.sub.6 O.sub.13+x as disclosed in U.S. Pat. No. 5,482,697 which is incorporated herein by reference in its entirety.
It would be advantageous to find vanadium oxides of greater discharge capacity and cycling life, as well as higher discharge voltage, at higher drain rates. To that end, the present invention is directed to the new cathode material Li.sub.x V.sub.5 O.sub.13, its method of manufacture and its use in solid secondary lithium electrochemical cells.